Abstract—This paper presents an approach to improve quality of service parameters over a delay tolerant network (DTN), which comprises of multiple message ferries, cluster heads of node clusters, and regular nodes. Intra-cluster routing is done via the mediation of cluster head; inter-cluster routing is done with the help of message ferries. This approach forms a structure capable to adapt dynamically to changes in the mobile environment. We provide also an asynchronous algorithm that will minimize the number of messages replicated and the network resources in general. Finally, we will present the simulation results demonstrating the effectiveness of the topology and routing protocol, particularly for high-density network nodes. Keywords— Delay Tolerant Networks DTN, Topology, Message Ferry, Hierarchy Routing, QoS. I. INTRODUCTION delay tolerant networking (DTN), as described in [1] is a kind of MANET network Mobile Ad-hoc Networks. It consists of a set of self-organized stations fully decentralized, forming an autonomous network, dynamic and without pre- existing infrastructure. These stations communicate with each other through a radio interface. Only the elements that exist in the transmission range are able to communicate directly with each other. Otherwise, communication between the components takes place by connecting the close messages until the destination is reached. In this case, it is not easy to find an efficient routing between distant elements. The mobility of stations and the lack of infrastructure have a significant impact on connectivity in such networks. Therefore, the topology of MANET network is rarely, if never, connected and the message delivery must be tolerant to delay [2, 3]. Intermittent connectivity, asymmetric flow, high error rate, long or variable delivery delay, extensive networks and high mobility of nodes characterize a DTN network. This latter This work was supported by Department of Computer Science, Faculty of Sciences and Technology Errachidia, Morocco. El Arbi Abdellaoui Alaoui, Department of Computer Science, Faculty of Sciences and Technology Errachidia, Morocco (Phone: +212665244247; e- mail: abdellaoui.e@ gmail.com). Prof. Said Agoujil, Department of Computer Science, Faculty of Sciences and Technology Errachidia, Morocco (e-mail: agoujil@gmail.com). Prof. Moha Hajar, Department of , Faculty of Sciences and Technology Errachidia, Morocco (e-mail: moha_hajjar@yahoo.fr). Prof. Youssef Qaraai, Department of Computer Science, Faculty of Sciences and Technology Errachidia, Morocco (e-mail: qaraai_youssef@yahoo.fr). creates new problems such as frequent disconnection, low communication rate, modest resources and limited energy source. These factors make the network spread on a large- scale, and therefore the delivery delay is very long and the delivery rate is potentially low. Thus, the choice of a technique for transmitting messages is then essential to ensure a great autonomy to these networks which are typically deployed in hostile or inaccessible areas. The objective of this work is to solve effectively this problem of delivering information between different nodes of the network. Some parameters must be taken into account in order to save the bandwidth, the scarce radio resources, etc. The designed protocol must adapt to the increased number of participants and their mobility, so that they can function correctly. Bearing in mind this problem, our approach to solve this problem is based on the idea of structuring and organizing the network before disseminating information by acting on the parameters to obtain proper network topology. The presence of such structure would reduce the impact of mobility, optimize both the delivery delay and delivery rate, particularly in the large-scale DTN networks and simplify routing. Indeed, a DTN network can be used to ensure reliable transmission in hostile networks with a very long delivery delay and intermittent connectivity. To facilitate communication and optimize the tasks that involve multiple nodes at once, a network organization is required. This organization is guaranteed by the establishment of a logical topology in the network that allows imposing rules and constraints governing the operation of the network and the collaboration between the different nodes, especially when the destination is not in the same region of the source. It is noteworthy to mention that the rest of this article is organized as the following: In Section II, we provide a background of the topology control in ad hoc networks and, in particular, the DTN networks. Then, in Section III, we provide a system model and problem statement. Then, we describe in section IV the model of the DTN routing hierarchical topology (DRHT). In Section V is devoted to the model of the success probability of delivery for a bundle with specific TTL and the average duration of inter-contact. In Section VI, we will describe the simulation environment and we will present the obtained results to assess the performance of the used topology control DRHT compared to Maxprop [4] protocols and Epidemic [5], Spray and Wait [6]. Finally, in Section VII, we present a conclusion. Improving the Delivery Rate of Data with : DTN Routing Hierarchical Topology (DRHT) El Arbi Abdellaoui Alaoui, Said Agoujil, Moha Hajar and Youssef Qaraai A INTERNATIONAL JOURNAL OF COMMUNICATIONS Volume 10, 2016 ISSN: 1998-4480 95